I was so surprised that I totally didn't get a screencap, but this happened while I was fishing at/near the lonely rock on the docks by Willy's place. I'd been fishing for several game hours, minding my own business, when an alien pokes its head out of the water. Then it swims off. Was just like O_O Did not see that coming. (Unmodded instance of year 1.)
I haven't seen that yet except in the wiki. Stuff like that is so frickin' COOL. I wonder if we'll see more in the next update.
Oh, thanks everyone! Mermaids are really ugly then, but don't tell them I said that. >_> Krobus might be impressed. This game is just full of surprises.